Wind power plants or wind farms generally include many individual wind turbines. Power generated by the wind turbines forms the total power delivered by the wind farm to a utility system or grid. The wind farm usually delivers the generated power to the grid through a Point of Common Coupling (PCC).
When there is a fault in the grid, the wind farm is usually disconnected from the grid to protect its wind turbines from sudden surge of current which may damage the components of the turbines. When the fault is cleared, the wind farm, and hence the wind turbines, is re-connected to the grid again to supply power thereto.
With increasing penetration of wind power generation, the disconnecting of the wind farm from the grid is no longer acceptable by grid operators. This is because there is a possibility of voltage collapse in the recovery phase after the fault is cleared due to high reactive power consumption and loss of synchronism. Grid operators in many countries now require wind farm operators to comply with certain grid requirements specified in grid codes before they are allowed to connect to the grid. Grid requirements vary in different countries, but they have a common aim of permitting the development, maintenance and operation of a coordinated, reliable and economical transmission or distribution system.
Grid codes typically require that wind turbines should be able to ride-through a fault causing the voltage at PCC to decrease to, for example 0.2 pu with duration of 0.5 seconds. In addition, grid codes also typically require reactive current contribution from individual wind turbines and/or wind farms during such grid faults.
In order to comply with grid requirements, wind turbines usually have solutions which enable the turbines to control the generation of reactive power. Thus when there is a grid fault causing the grid voltage to fall, the wind turbines can increase their reactive current output. The total increase in the reactive current from the wind turbines can be injected into the grid through the PCC of the wind farm to stabilize the grid.
U.S. Pat. No. 6,924,565 discloses a network of variable speed wind turbine generator systems. Each generator is able to generate real power and reactive power, and includes a system controller coupled to the generators to control the real and reactive power generated by the generators based on thermal capability and/or voltage limits of the individual generators. Thus, the network of generator systems is able to provide commanded real and reactive power with a closed-loop voltage system. In this patent document, a voltage controller monitors the PCC between the wind turbine generator system and the utility grid. Based on measurements, reactive power commands are transmitted to the individual generators to generate the required reactive power for the wind turbine generator system. Thus, the system provides a closed loop control.
Thus, aspects in accordance with embodiments of the invention are directed to providing an improved solution to control the current provided at the PCC during a grid fault.